Frictional disk-type side clutches and brakes are well suited for steering a vehicle because the clutches and brakes do not require a large space and because one may easily operate the clutches and brakes by applying an operating force to them. Thus, these clutches and brakes easily turn the vehicle at a desired radius.
Such side clutches and side brakes are incorporated in a vehicle power transmission between an axle-driving power output shaft and left and right wheel axles. In the past, left and right clutch shafts for associating left and right side clutches and brakes have been provided separately from the axle-driving power output shaft.
That is, as shown in, for example, Japanese Utility Model Publication No. 60-23253, left and right clutch shafts are disposed coaxially with an axle-driving output shaft at opposite sides of the output shaft. To one and the other ends of the output shaft are fixedly secured left and right clutch housings which extend towards left and right clutch shafts, respectively. Each of the left and right side clutches is disposed within each of the left and right clutch housings and is fashioned into a frictional disk type having opposite sets of frictional elements which are slidably but non-rotatably supported respectively by each clutch housing and by each of the left and right clutch shafts. At the outer sides of such left and right side clutches are disposed left and right side brakes of a frictional disk type each of which is fashioned to have opposite sets of frictional elements supported respectively by a transmission casing, or alternatively by a separate brake casing, and by each clutch shaft.
The structure referred to above requires a lengthy transmission casing due to separate clutch shafts disposed at opposite sides of the output shaft and due to the side by side arrangement of respective side clutches and side brakes which arrangement requires prolonged clutch shafts.
For steering a vehicle, the clutch and brake at one side of a clutch and brake assembly are usually operated using a common operating mechanism so that first, the clutch is disengaged and then the brake is actuated. The clutch and brake at each side are spaced axially on each of the clutch shafts according to the prior art, and they necessarily require separate clutch-disengaging and brake-actuating mechanisms. Thus, a timing mechanism required for operating the clutch and brake in order must be included in the clutch/brake-operating mechanism. A clutch spring which is associated with each side clutch for keeping the clutch normally in its engaged state can not be used also as a return spring for preventing a spontaneous or unexpected actuation of each side brake, because a brake-actuating mechanism is provided separately from a clutch-disengaging mechanism. Consequently, both of the clutch spring and brake return spring are provided which will make clutch/brake-operation heavy.